Generally, in the existing PBB-VPLS network, user service bridge domain VPLS (I-VPLS) instances with Hub and Spoke topology (also referred to as rooted multipoint tree topology) can work by configuring multiple provider backbone bridge domain VPLS (B-VPLS) instances, wherein each B-VPLS instance can only support the I-VPLS instances having the same or compatible root site and tree topology.
FIG. 1 shows a schematic diagram of a technical solution which supports multiple I-VPLS instances with different root sites and tree topologies in the existing PBB-VPLS network. As shown in FIG. 1, the PBB-VPLS network is based on an IP/MPLS network, and the provider edge equipment (PE) includes user side provider edge equipments U-PE1, U-PE2, U-PE3, U-PE4 and network side provider edge equipments N-PE1, N-PE2, wherein the N-PE1 receives data packets from the U-PE1 and U-PE2, and the N-PE2 receives data packets from the U-PE3 and U-PE4. Each of the user side provider edge equipments is configured with three I-VPLS instances, wherein two I-VPLS instances I1 and I2 have the same root site and tree topology, and the other one I-VPLS instance I3 has the different root site and tree topology from I1 and I2. Thus, each of the network side provider edge equipments and the user side provider edge equipments is configured with two B-VPLS instances B12 and B3, wherein the I-VPLS instances I1 and I2 are coupled to the B-VPLS instance B12, and the I-VPLS instance I3 is coupled to the B-VPLS instance B3, and the B-VPLS instances at the network side provider edge equipment and the corresponding B-VPLS instances at the user side provider edge equipment are coupled to each other via pseudo wires.
To implement a specific tree topology in an I-VPLS, that is, to control forwarding of the data packets between the different sites for one VPLS instance, Split Horizon Group (SHG) technique is employed. In FIG. 1, the pseudo wire coupling a pair of B-VPLS instances B12 at the N-PE1 and U-PE1 and the pseudo wire coupling a pair of B-VPLS instances B12 at the N-PE1 and U-PE2 (represented with dashed line respectively) belong to the same SHG, the pseudo wire coupling a pair of B-VPLS instances B12 at the N-PE1 and N-PE2 and the pseudo wire coupling a pair of B-VPLS instances B12 at the N-PE2 and U-PE3 (represented with dashed line respectively) belong to the same SHG; and the pseudo wire coupling a pair of B-VPLS instances B3 at the N-PE2 and U-PE3 and the pseudo wire coupling a pair of B-VPLS instances B3 at the N-PE2 and U-PE4 (represented with dot dash line respectively) belong to the same SHG, the pseudo wire coupling a pair of B-VPLS instances B3 at the N-PE1 and N-PE2 and the pseudo wire coupling a pair of B-VPLS instances B3 at the N-PE1 and U-PE2 (represented with dot dash line respectively) belong to the same SHG.
The SHG technique is well known in the art. With this technique, a multipoint-to-multipoint full mesh topology between the sites of the VPLS network can be effectively transformed into a rooted multipoint tree topology. Namely, only communication between a root node and a leaf node is allowed, while communication between leaf nodes is forbidden.
However, due to having to configure multiple B-VPLS instances, the existing technical solution shown in FIG. 1 has following problems: The B-VPLS instances are usually regarded as the infrastructure of the backbone connection, and should be stable and unaffected by user access as much as possible, and the effect due to the user access should be absorbed by the I-VPLS instances configured at the user side provider edge equipments. However, when accessing by the user with the I-VPLS instances having new root sites and tree topologies, since one B-VPLS instance can only serve the I-VPLS instances with the same or compatible root site and tree topology, it is inevitable to configure new B-VPLS instance. Thus, the existing technical solution cannot maintain the structure of the backbone network stable, thereby increasing operation cost.
In the existing technical solution, the tree topology for forwarding data packets is statically determined by the SHG. Once the SHG is configured, the tree topology is fixed, and any I-VPLS instance that does not comply with the tree topology is served by other B-VPLS instance. Therefore, it is not possible for the existing technical solution to support multiple I-VPLS instances with different root sites and tree topologies by one B-VPLS instance.